Recovery Strategy for the Butler's Gartersnake (Thamnophis butleri) in Canada - Butler's Gartersnake
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PROPOSED Species at Risk Act
Recovery Strategy Series
Recovery Strategy for the Butler’s
Gartersnake (Thamnophis butleri) in Canada
Butler’s Gartersnake
2016
Recommended citation:
Environment Canada. 2016. Recovery Strategy for the Butler’s Gartersnake (Thamnophis
butleri) in Canada [Proposed]. Species at Risk Act Recovery Strategy Series. Environment
Canada, Ottawa. vi + 47 pp.
For copies of the recovery strategy, or for additional information on species at risk, including the
Committee on the Status of Endangered Wildlife in Canada (COSEWIC) status reports,
residence descriptions, action plans, and other related recovery documents, please visit the
Species at Risk (SAR) Public Registry1.
Cover illustration: © Daniel Noble and Jonathan Choquette
Également disponible en français sous le titre
« Programme de rétablissement de la couleuvre à petite tête (Thamnophis butleri) au Canada
[Proposition] »
© Her Majesty the Queen in Right of Canada, represented by the Minister of the Environment,
2016. All rights reserved.
ISBN
Catalogue no.
Content (excluding the illustrations) may be used without permission, with appropriate credit to
the source.
1
http://www.registrelep-sararegistry.gc.ca
Recovery Strategy for the Butler’s Gartersnake 2016
Preface
The federal, provincial, and territorial government signatories under the Accord for the
Protection of Species at Risk (1996) 2 agreed to establish complementary legislation and
programs that provide for effective protection of species at risk throughout Canada. Under the
Species at Risk Act (S.C. 2002, c.29) (SARA), the federal competent ministers are responsible
for the preparation of recovery strategies for listed Extirpated, Endangered, and Threatened
species and are required to report on progress five years after the publication of the final
document on the SAR Public Registry.
The Minister of the Environment is the competent minister under SARA for the Butler’s
Gartersnake and has prepared this strategy, as per section 37 of SARA. To the extent possible,
it has been prepared in cooperation with the Province of Ontario.
Success in the recovery of this species depends on the commitment and cooperation of many
different constituencies that will be involved in implementing the directions set out in this
strategy and will not be achieved by Environment Canada, or any other jurisdiction alone.
All Canadians are invited to join in supporting and implementing this strategy for the benefit of
Butler’s Gartersnake and Canadian society as a whole.
This recovery strategy will be followed by one or more action plans that will provide information
on recovery measures to be taken by Environment Canada and other jurisdictions and/or
organizations involved in the conservation of the species. Implementation of this strategy is
subject to appropriations, priorities, and budgetary constraints of the participating jurisdictions
and organizations.
The recovery strategy sets the strategic direction to arrest or reverse the decline of the species,
including identification of critical habitat to the extent possible. It provides all Canadians with
information to help take action on species conservation. When the recovery strategy identifies
critical habitat, there may be future regulatory implications, depending on where the critical
habitat is identified. SARA requires that critical habitat identified within federal protected areas
be described in the Canada Gazette, after which prohibitions against its destruction will apply.
For critical habitat located on federal lands outside of federal protected areas, the Minister of the
Environment must either make a statement on existing legal protection or make an order so that
the prohibition against destruction of critical habitat applies. For critical habitat located on non-
federal lands, if the Minister of the Environment forms the opinion that any portion of critical
habitat is not protected by provisions in or measures under SARA or other Acts of Parliament,
and not effectively protected by the laws of the province or territory, SARA requires that the
Minister recommend that the Governor in Council make an order to extend the prohibition
against destruction of critical habitat to that portion. The discretion to protect critical habitat on
non-federal lands that is not otherwise protected rests with the Governor in Council.
2
http://registrelep-sararegistry.gc.ca/default.asp?lang=en&n=6B319869-1#2
i
Recovery Strategy for the Butler’s Gartersnake 2016
Acknowledgments
Jennifer Brownlee developed the first draft of the Butler’s Gartersnake recovery strategy under
contract to Environment Canada, Canadian Wildlife Service – Ontario (EC, CWS-ON). The draft
strategy was updated by Rebecca Carter under contract to EC, CWS-ON. Ken Tuininga led the
completion of this recovery strategy with assistance from Lauren Strybos, Krista Holmes,
Christina Rohe, Marie-Claude Archambault, Angela Darwin and Graham Bryan, (EC, CWS-ON)
and Kari Van Allen and Megan Eplett (formerly EC, CWS-ON). Contributions from
Lesley Dunn and Madeline Austen (EC, CWS-ON) are also gratefully acknowledged.
Al Sandilands (Gray Owl Environmental Inc.), Daniel Noble (Macquarie University), Frederick
Schueler (Bishop Mills Natural History Centre), and Jonathan Choquette (SCC Ecological)
provided comments and advice during the development of this document. Joe Crowley,
Jay Fitzsimmons, Leanne Jennings, Aileen Wheeldon, (Ontario Ministry of Natural Resources
and Forestry (OMNRF) and Mike Oldham (Natural Heritage Information Centre, OMNRF)
reviewed and provided comments and advice during the development of this document.
Megan Hazell (AMEC Foster Wheeler), Wayne King (LGL Ltd.) and Barbara Macdonnell
(Ministry of Transportation Ontario) also reviewed and provided comments during the
development of the document and were extremely helpful in sharing data based on the extensive
monitoring work completed for the requirements of the Endangered Species Act, 2007 permits
for the development of the Right Honourable Herb Gray Parkway.
Acknowledgment and thanks are given to all other parties that provided advice and input used to
help inform the development of this recovery strategy including various Aboriginal organizations
and individual citizens, and stakeholders who provided input and/or participated in consultation
meetings.
ii
Recovery Strategy for the Butler’s Gartersnake 2016
Executive Summary
Butler’s Gartersnake is listed as Threatened on Schedule 1 of the federal Species at Risk Act. The
species is listed as Endangered in Ontario under the provincial Endangered Species Act, 2007
(ESA 2007). Butler’s Gartersnake (Thamnophis butleri) is a small gartersnake with three distinct
yellow to orange longitudinal stripes running from head to tail over a brown body. A dark checkered
pattern is evident running alongside its stripes. Like most other small Canadian snakes, this species
has not been well studied. Butler’s Gartersnake is often confused with two other gartersnakes
coexisting in its range, both belonging to the same genus, Thamnophis. These similar species are the
Common Gartersnake (T. sirtalis) and the Eastern Ribbonsnake (T. sauritus). Butler’s Gartersnake is
shorter in total length (38 – 51 cm), more docile and has a unique pattern and position of side stripes
in comparison to these species.
In Canada, Butler’s Gartersnake is restricted to Ontario where it has recently been found in two
regions: Windsor-Sarnia (Essex, Chatham-Kent, Lambton Counties and Walpole Island) and
Luther Marsh (Dufferin and Wellington Counties). Further surveys are required to determine if it still
exists in other areas including: Skunk’s Misery (Lambton and Middlesex Counties), Parkhill
(Middlesex County) and additional locations in the Windsor-Sarnia region. In the United States,
Butler’s Gartersnake is restricted to the Great Lakes Region and is found within four states:
Wisconsin, Ohio, Indiana, and Michigan.
Butler’s Gartersnake is found in grasslands, old fields, disturbed sites, urban and industrial sites and
tallgrass prairie where a dense cover of grasses or herbs and a heavy thatch layer are present. The
species is often found in close proximity to wet areas such as small marshes (seasonally dry), swales,
and small bodies of water located in vacant urban lots (industrial lands), parks and tallgrass prairie
remnants.
The major threats contributing to Butler’s Gartersnake decline are ongoing habitat loss, degradation
and fragmentation, due to urban, industrial and road development as well as agricultural expansion.
There are unknowns regarding the feasibility of recovery of the Butler’s Gartersnake. The population
and distribution objective for Butler’s Gartersnake is to maintain the current abundance and
distribution of all extant subpopulations. Where biologically and technically feasible, the distribution
and abundance of extant subpopulations should be increased and habitat connectivity between local
subpopulations improved. The broad strategies to be taken to address the threats to the survival and
recovery of Butler’s Gartersnake are presented in the section on Strategic Direction for Recovery
(Section 6.2).
There are several locations that may still support Butler’s Gartersnake, however these locations have
not been surveyed recently or adequately and/or there is a lack of certainty in the data needed to
identify critical habitat. For this reason, critical habitat for Butler’s Gartersnake has only been
partially identified in this recovery strategy. Critical habitat is identified for 27 extant locations in
Ontario and occurs within the geographic regions of Windsor-Sarnia and Luther Marsh. The
Schedule of Studies (Section 7.2) outlines the activities required to identify additional critical habitat
necessary to support the population and distribution objectives for this species.
One or more action plans for Butler’s Gartersnake will be completed by December 2023.
iii
Recovery Strategy for the Butler’s Gartersnake 2016
Recovery Feasibility Summary
Based on the following four criteria that Environment Canada uses to establish recovery
feasibility, there are unknowns regarding the feasibility of recovery of the Butler’s Gartersnake.
In keeping with the precautionary principle, this recovery strategy has been prepared as per
section 41(1) of SARA, as would be done when recovery is determined to be feasible.
1. Individuals of the wildlife species that are capable of reproduction are available now or in the
foreseeable future to sustain the population or improve its abundance.
Yes. There are currently 27 to 38 extant 3 locations 4 of Butler’s Gartersnake in Canada, which
occur within four geographic regions. The species is frequently locally abundant where it
does occur and may be the most common snake species at some locations. Most local
subpopulations are small, though exact numbers may not be known, and may be threatened
by negative genetic effects of small population size and demographic stochasticity as well as
numerous other threats (COSEWIC 2010). However, there are several large subpopulations
of this species in Ontario that are capable of maintaining the species in the province
(COSEWIC 2010).
2. Sufficient suitable habitat is available to support the species or could be made available
through habitat management or restoration.
Unknown. In Ontario, sufficient suitable habitat is available to support the current
population. Walpole Island contains one of the largest remnant tracts of native prairie in
Ontario and as much as 10% of the Canadian population is believed to occur here
(Bowles 2005). This species is also found within Nature Reserves and Conservation Areas in
Ontario such as Ojibway Prairie (Windsor) and Luther Marsh (north of Guelph) and it may
also still exist in Skunk’s Misery, Parkhill and in additional locations in the Windsor-Sarnia
region (see Figure 2). It is also possible that in some urban areas, new habitat may be created
as abandoned industrial sites are allowed to naturalize (COSEWIC 2010). However, its
distribution, particularly for some urban subpopulations, is limited due to habitat
fragmentation and confined to a limited area of Southern Ontario. This results in
subpopulations being isolated from one another, which can lead to a reduction in genetic
diversity and even inbreeding. Thus, maintaining connectivity between subpopulations is
crucial to the recovery of Butler’s Gartersnake.
3
Population/subpopulation which is considered to be still in existence.
4
Location: a geographically or ecologically distinct area in which a single threatening event can rapidly affect all
individuals of the taxon present. Throughout this document, the term ‘subpopulation” is considered synonymous
with the term “location” as used by the 2010 COSEWIC Status Report and the International Union for the
Conservation of Nature (IUCN 2010) (i.e., consideration for threats, distance, geographical separation and perceived
habitat connectivity between clusters of collecting sites (a collection site is defined as a specific place where a snake
was seen or collected. See Appendix B for more information on locations of Butler’s Gartersnake in Canada.
ivRecovery Strategy for the Butler’s Gartersnake 2016
3. The primary threats to the species or its habitat (including threats outside Canada) can be
avoided or mitigated.
Unknown. The primary threats to the species are urban, industrial and road development as
well as agricultural expansion. Some current and future development and agricultural
expansion in suitable Butler’s Gartersnake habitat can be avoided through stewardship,
co-operation with landowners, land managers and First Nations, land use management
practices and policy and regulations such as the recently implemented activities for the
Right Honourable Herb Gray Parkway. Snake barriers, monitoring coverboards, inspecting
key habitat features and working within timing windows have reduced impacts to snakes
during construction (AMEC Environment and Infrastructure, environmental consultants on
behalf of the Parkway Infrastructure Constructors and Windsor Essex Mobility Group 2013).
However, many local subpopulations exist in small and or isolated habitat fragments, in
urban areas with established road networks where mitigation may be difficult or impossible.
4. Recovery techniques exist to achieve the population and distribution objectives or can be
expected to be developed within a reasonable timeframe.
Yes. Standard techniques exist for monitoring and general habitat restoration (e.g., creation
of hibernacula, habitat enhancement). Land management practices have been developed to
provide agricultural, urban and industrial private land owners with the information necessary
to coexist with wildlife without polluting or destroying suitable habitat (e.g., Best
Management Practices such as implementing and maintaining wildlife corridors, controlling
invasive species such as European Common Reed (Phragmites australis australis),
maintaining open-canopy, dense ground-layer vegetation and avoiding activities that allow
the encroachment of woody vegetation (Tallgrass Ontario 2005; Savanta Inc. 2008;
Ontario Ministry of Natural Resources 2011; Mifsud 2014; Wisconsin Department of Natural
Resources 2014)). Research on many recovery techniques specific to Butler’s Gartersnake
was carried out to fulfill the Endangered Species Act, 2007 permit requirements for the
Right Honourable Herb Gray Parkway development including research that will involve
monitoring relative to eco-passages and culverts under roads.
vRecovery Strategy for the Butler’s Gartersnake 2016
Table of Contents
Preface ............................................................................................................................. i
Acknowledgments ............................................................................................................ii
Executive Summary ........................................................................................................ iii
Recovery Feasibility Summary ........................................................................................iv
1. COSEWIC Species Assessment Information .............................................................. 1
2. Species Status Information .......................................................................................... 1
3. Species Information ..................................................................................................... 2
3.1 Species Description .............................................................................................. 2
3.2 Population and Distribution ................................................................................... 3
3.3 Needs of the Butler’s Gartersnake ........................................................................ 7
3.4 Biological Limiting Factors .................................................................................... 9
4. Threats ...................................................................................................................... 11
4.1 Threats Assessment ........................................................................................... 11
4.2 Description of Threats ...................................................................................... 11
5. Population and Distribution Objectives ...................................................................... 14
6. Broad Strategies and General Approaches to Meet Objectives................................. 15
6.1 Actions Already Completed or Currently Underway ............................................ 15
6.2 Strategic Direction for Recovery ......................................................................... 17
6.3 Narrative to Support the Recovery Planning Table ............................................. 19
7. Critical Habitat ........................................................................................................... 19
7.1 Identification of the Species’ Critical Habitat ....................................................... 19
7.2 Schedule of Studies to Identify Critical Habitat ................................................... 33
7.3 Activities Likely to Result in the Destruction of Critical Habitat ............................ 34
8. Measuring Progress................................................................................................... 37
9. Statement on Action Plans ........................................................................................ 37
10. References ....................................................................................................... 38
Appendix A: Effects on the Environment and Other Species ........................................ 45
Appendix B: Subpopulations of Butler’s Gartersnake in Canada .................................. 46
viRecovery Strategy for the Butler’s Gartersnake 2016
1. COSEWIC* Species Assessment Information
Date of Assessment: November 2010
Common Name: Butler’s Gartersnake
Scientific Name: Thamnophis butleri
COSEWIC Status: Endangered
Reason for Designation: Most populations of this species occur in small, scattered habitat
remnants. Most are isolated so they are threatened by the negative genetic effects of small
population size and by demographic stochasticity5. Recent surveys have not detected the
species at several sites where they were formerly known. Road mortality, ongoing habitat loss
and fragmentation are also threats to this small specialized snake.
Canadian Occurrence: Ontario
COSEWIC Status History: Designated Special Concern in April 1999. Status re-examined
and designated Threatened in November 2001. Status re-examined and designated Endangered
in November 2010.
*Committee on the Status of Endangered Wildlife in Canada
2. Species Status Information
The global conservation rank for Butler’s Gartersnake (Thamnophis butleri) is Apparently
Secure 6 (G4) (NatureServe 2014). In the United States, it is ranked nationally as Apparently
Secure (N4), and subnationally as Critically Imperiled 7 in Indiana (S1), Vulnerable 8/Apparently
Secure in Wisconsin (S3S4), Apparently Secure in Michigan (S4), and has not been officially
ranked in the state of Ohio (SNR). In Canada, Butler’s Gartersnake is ranked Imperiled both
nationally (N2) and provincially (S2) in Ontario (NatureServe 2014).
Butler’s Gartersnake is currently listed as Threatened 9 on Schedule 1 of the federal Species at Risk
Act (SARA) and is listed as Endangered 10 under Ontario’s Endangered Species Act, 2007
(ESA 2007). Approximately 16% of the global range occurs in Canada (COSEWIC 2010).
5
Demographic stochasticity refers to the variability of population growth rates arising from related random events
such as birth rates, death rates, sex ratio, and dispersal. It is particularly important for small populations because it
increases the probability of extirpation.
6
Uncommon but not rare; some cause for long-term concern due to declines or other factors.
7
Extreme rarity or because of some factor(s) such as very steep declines making it especially vulnerable to extirpation
from jurisdiction.
8
Due to a restricted range, relatively few populations, recent and widespread declines, or other factors making it
vulnerable to extirpation.
9
A wildlife species that is likely to become endangered if nothing is done to reverse the factors leading to its
extirpation or extinction.
10
Endangered: a native species facing imminent extinction or extirpation.
1Recovery Strategy for the Butler’s Gartersnake 2016
3. Species Information
3.1 Species Description
Butler’s Gartersnake is a small snake typically ranging from 38 to 51 cm in length with a
maximum recorded length of 73.7 cm (Minton 1972 as cited in Rossman et al. 1996). It has a
small head only slightly broader than the neck (Rossman et al. 1996) and a tail that is generally
20 to 25% of its total length (Sandilands 2001). Bearing the characteristic striped pattern of
gartersnakes, Butler’s Gartersnake has three longitudinal yellow to orange stripes, one dorsal 11 and
two lateral 12 (Conant and Collins 1991; Rossman et al. 1996; Ernst and Ernst 2003). The dorsal
stripe may also be white to cream in colour. The lateral stripes are centred on the 3rd scale row and
at least anteriorly, they extend onto scale rows 2 and 4 (Ernst and Barbour 1989; Ernst and
Ernst 2003; COSEWIC 2010). In some regions, the lateral stripes may be centred on the third scale
row and only encompass half of the second row. The whitish underbelly is divided from the lateral
stripe by a broad chestnut coloured stripe along the first lateral scale row and the upper edges of
the ventral 13 scales (COSEWIC 2010). The back may range from olive-brown or chestnut to black.
Butler’s Gartersnake may be confused with two other Thamnophis species occurring in Ontario,
the Common Gartersnake (T. sirtalis) and the Eastern Ribbonsnake (T. sauritus) which both occur
in southwestern Ontario (Sandilands 2001; COSEWIC 2010). In the case of the Eastern
Ribbonsnake, the lateral stripes are on rows 3 and 4, while for the Common Gartersnake they are
on rows 2 and 3. The Common Gartersnake and Eastern Ribbonsnake have larger heads and more
pronounced necks than the Butler's Gartersnake. The Eastern Ribbonsnake also has a distinct white
crescent in front of the eye, is more slender and has a longer tail. Further, the Eastern Ribbonsnake
does not occur in most of the areas in southwestern Ontario where Butler’s Gartersnakes are found
(Ontario Nature 2014).
Like many other snake species, Butler’s Gartersnake avoids mid-day sun and becomes active in
the morning and evening during midsummer (Logier 1939; Catling and Freedman 1980(a); Ernst
and Ernst 2003). Butler’s Gartersnakes are non-aggressive, and will quickly seek shelter in thick
grass thatch if disturbed (Ernst and Barbour 1989; Ernst and Ernst 2003; COSEWIC 2010).
Although Butler’s Gartersnake can move quickly in grassy areas, when travelling over hard
surfaces it moves much more slowly having to slither sideways, in a “side-winding” motion
(Sandilands 2001; Ontario Nature 2011). Butler’s Gartersnake also has a prehensile 14 tail allowing
it to wrap around vegetation or other objects to avoid predation (Environment Canada 2014).
11
The upper side or back of an animal
12
Situated on one side or other of the body
13
Of, on, or relating to the underside of an animal
14
Capable of grasping.
2Recovery Strategy for the Butler’s Gartersnake 2016
3.2 Population and Distribution
Butler’s Gartersnake is endemic to North America where its range is considered one of the most
restricted of all snake species (Sandilands 2001); its range is limited to an area near the lower
Great Lakes in the United States (south-eastern Wisconsin, Indiana, Ohio and the Lower Peninsula
of Michigan) and Canada (southern Ontario) (Nature Serve 2013) (Figure 1). The global range is
estimated to be between 20,000 and 200,000 km2 (Nature Serve 2013). Even though Butler’s
Gartersnake subpopulations are somewhat disjunctive 15 within their range, in many cases this
species is locally abundant (Conant 1951; Conant and Collins 1991; Rossman et al. 1996). Due to
its affiliation with prairie and grassland habitat and its current disjunct distribution, it is presumed
that Butler’s Gartersnake’s former Canadian range included previously occupied sites between
currently known locations (COSEWIC 2010).
The current Canadian range of Butler’s Gartersnake is restricted to four geographically isolated
regions in southwestern Ontario. Two regions: Windsor-Sarnia (Essex, Chatham-Kent, and
Lambton Counties) and Luther Marsh (Dufferin and Wellington Counties) contain recent
occurrence observations of Butler’s Gartersnake. The species is also historically known to occur in
Skunk’s Misery (Lambton and Middlesex Counties) and Parkhill (Middlesex County) (COSEWIC
2010), however, further surveys are needed to confirm the species’ presence in these two areas.
The species is considered extirpated from a fifth region near Rondeau Provincial Park.
Within these regions, 48 locations of Butler’s Gartersnake have been documented (Figure 2,
Appendix B). For the purposes of this report, the term ‘location’ is used synonymously with the
term ‘subpopulation’. Six are considered extirpated 16 and four are considered historical (i.e., not
observed in >20 years). The number of extant subpopulations is believed to be between 27 and 38.
The uncertainty in the number of extant subpopulations is due to the fact that at seven locations,
which were last visited in 2009 (including Walpole Island), surveyors did not find any Butler’s
Gartersnakes, although suitable habitat appears to be available. An additional three locations have
lost significant portions of their habitat (COSEWIC 2010, Appendix B: locations 11, 14, 40) and
additional surveys are required to confirm the status at these locations.
Seven locations visited in 2009 are new locations not previously noted in the literature. New
locations have not been assessed by the Natural Heritage Information Centre and in the future, the
enumeration of subpopulations may better align with element occurrence information. More
recently, Noble et al. (2013) suggested that Butler’s Gartersnakes in Windsor, Sarnia, and
Luther Marsh consist of four to five genetically distinct clusters which are subdivided into three or
four subpopulations but it is not clear how the known locations are designated within those
clusters.
Throughout its current distribution, Butler’s Gartersnakes are mainly scattered in small,
fragmented locations. No snakes have been encountered at Skunk’s Misery from 1989-2009
despite several targeted searches. Only one snake is known from Parkhill (1992), and this area was
15
Discontinuous or separated from other subpopulations or populations.
16
Population/subpopulation which was previously known to occur (i.e., for which there is historical record), but that
no longer exists.
3Recovery Strategy for the Butler’s Gartersnake 2016
not searched in 2009 when other surveys for Butler’s Gartersnake were conducted in Ontario
(COSEWIC 2010). Further surveying, particularly in the spring, is required to confirm the
presence/absence of the species at Skunk’s Misery, Parkhill, Walpole Island and an additional
12 locations within the Windsor-Sarnia geographic region (COSEWIC 2010; J. Choquette pers.
comm. 2014).
Several effective methods for detecting this secretive species enabled reliable estimates for a
few Windsor subpopulations during the Herb Gray Parkway (HGP) project. 17 Radio telemetry
using specialized transmitters, passive integrated transponder (PIT) tagging, a mark-recapture
program and hibernacula enclosure fences to confirm hibernacula locations and snake use were
employed. Through modeling of data collected using these methods, this project produced an
estimate of around 550 individuals for HGP monitored areas in 2013 (LGL 2010; AMEC
Environment and Infrastructure, environmental consultants on behalf of the Parkway Infrastructure
Constructors and Windsor Essex Mobility Group (AMEC) 2012, 2013, 2014).
Currently, the long term survival of Butler’s Gartersnake in Ontario is uncertain. In 2010 Butler’s
Gartersnake was reassessed from Threatened to Endangered by COSEWIC due to its small overall
distribution in Canada, ongoing habitat loss including fragmentation and proposed development at
many locations, and the decline and downward trend in the number of known local subpopulations.
Most local subpopulations exist in small and or isolated habitat fragments and may be threatened
by negative genetic effects of small population size and demographic stochasticity
(COSEWIC 2010).
17
The Rt. Hon. Herb Gray Parkway is a major highway infrastructure project that will form part of the transportation
corridor connecting Highway 401 in Ontario to Interstate 75 in Michigan.
4Recovery Strategy for the Butler’s Gartersnake 2016
Figure 1. Global Distribution of Butler’s Gartersnake (Modified from NatureServe 2014).
5Recovery Strategy for the Butler’s Gartersnake 2016
Figure 2. Location of Butler's Gartersnake subpopulations in Canada (modified from COSEWIC 2010).
6Recovery Strategy for the Butler’s Gartersnake 2016
3.3 Needs of the Butler’s Gartersnake
Butler’s Gartersnake is thought to be originally associated with post-glacial prairie in the
Great Lakes region over 7,000 years ago (Schmidt 1938; Smith 1957; Bleakney 1958;
Environment Canada 2014). This species has persisted in prairie remnants dominated by grasses
including Big Bluestem (Andropogon gerardii) and Little Bluestem (Schizachyrium. scoparium) in
southwestern Ontario (Sandilands 2001), though many populations now persist in highly altered
human landscapes (e.g., fields, parklands, etc.). COSEWIC (2010) also indicates that all Butler’s
Gartersnake locations (with the exception of Luther Marsh) coincide with remnants of tallgrass
prairie and oak savanna habitats which are critically imperiled in Ontario. Only 2.4 percent of
northern tallgrass prairie remains in all of North America today (Samson et al. 2004), with less
than 1 percent remaining in Ontario (Bakowsky and Riley 1994; Catling and Brownell 1999;
Catling 2008).
General Habitat Needs
Butler’s Gartersnake habitat in Ontario is characterized by open areas with dense grasses
(e.g., cultural meadows, grasslands, old fields, tallgrass prairie communities) in close proximity to
wet areas (i.e., small marshes, seasonal wet areas, small bodies of water) (Logier 1939; Planck and
Planck 1977; Conant and Collins 1991; COSEWIC 2010). Dense grass cover with a heavy thatch
layer is essential to its habitat, as the thatch layer allows Butler's Gartersnakes to move around in
search of food under cover from predators (Planck and Planck 1977). In some areas, the species
persists in early successional habitat where open grasslands are supporting shrubs and trees
(Logier 1939). Butler’s Gartersnake is also known to occur along treed edges and in vacant lots,
small parks and abandoned sites in urban areas (Ernst and Barbour 1989; Rossman et al. 1996;
Ernst and Ernst 2003; AMEC 2014).
Live Birthing Habitat
Core use areas of Butler’s Gartersnake are typically associated with live birthing habitat or open
basking habitat where females spend large amounts of time prior to giving birth (AMEC 2012;
2013). Butler’s Gartersnakes are ovoviviparous (give birth to live young rather than lay eggs) and
have between 4 and 20 young by early July to mid-September (Vogt 1981; Ernst and Ernst 2003;
LGL and URS 2010). During the first two weeks of July, gravid 18 females may suddenly change
behaviour and move out of previous activity areas in rapid linear movements to live birthing sites
(LGL 2011; AMEC 2012, 2013, 2014); sometimes travelling over 200 m outside their activity
areas (LGL 2010). Others were documented, also in multiple years, basking in habitats adjacent to
live birthing sites just prior to giving birth (AMEC 2012, 2013, 2014). Live birthing habitat for
Butler’s Gartersnake consists of lowland areas or wet depressions surrounded by higher and drier
land. Drier areas typically include shrub or tree cover along the edges of wet depressions, and may
include wetland indicator plant species typically found in swamps and marshes (LGL 2011;
AMEC 2012, 2013, 2014). AMEC (2012, 2013, 2014) confirmed fidelity to live birthing areas
across successive years and in multiple monitoring zones, as part of the HGP monitoring, where
the same live birthing areas were used by the same Butler’s Gartersnake population.
18
Internally carrying developing young or eggs.
7Recovery Strategy for the Butler’s Gartersnake 2016
Hibernation Habitat
Butler’s Gartersnakes commonly hibernate individually through the cold winter months across
their range, beginning hibernation in mid-September and not emerging until early April
(Conant 1951; Wright and Wright 1957; LGL 2010). Hibernacula 19 recorded in Ontario include:
Devil Crayfish (Cambarus diogenes; also known as Chimney Crayfish or Meadow Crayfish)
burrows, small mammal burrows, drains, log piles, and other underground sites (LGL 2010;
AMEC 2012, 2013, 2014). Radio-tracked Butler’s Gartersnakes largely used crayfish burrows,
often trying several burrows in the fall before settling on one for the winter (AMEC 2012, 2013,
2014). Hibernacula are usually associated with wetland habitats (open areas or more treed areas) or
open water (drainage ditches), as both Chimney and Meadow Crayfish require certain water levels
in areas where they create their burrows (i.e., must be able to reach ground water during periods of
drought) (Bovbjerg, 1952; Hobbs 1989). To date, Butler’s Gartersnakes have not yet been
observed using the artificial hibernacula created to mitigate impacts to individuals captured during
construction of the HGP (AMEC 2013); though several relocated Butler’s Gartersnakes have
found new hibernacula in the habitats to which they were moved, suggesting that adaptation to
new habitats is possible for some individuals. The Wisconsin Department of Natural Resources
(WDNR) identified several man-made structures as providing hibernacula for Butler’s
Gartersnake, such as old building foundations, sink holes, and improperly capped landfills and
dumps (Freedman and Catling 1978; WDNR 2005; WDNR 2014).
Foraging Habitat
Butler’s Gartersnakes spend most of their time during active months, generally April to
September, foraging in long grasses found in tallgrass prairie, cultural thickets, cultural meadows,
and meadow marshes (Planck and Planck 1977; LGL 2010; AMEC 2012). The species’ preference
for open grassland habitat with access to wetter areas may be related to its preferred prey,
earthworms (Catling and Freedman 1980(a); Lyman-Henley and Burghardt 1995; W. King
pers. comm. 2014).
Thermoregulation/Mating Habitat
Butler’s Gartersnakes regulate their body temperature by basking and cooling throughout the day
(Huey and Kingsolver 1989; Grant 1990). In order to elevate their body temperature, Butler’s
Gartersnakes seek out open spaces in vegetation, edges of water, the top of logs, coverboards,
grass thickets, brushpiles and clusters of vegetation up to a metre above the ground (LGL 2010;
AMEC 2013). The species has also been observed basking on gravel roads on cool evenings
(C. Campbell and F.W. Schueler pers. comm. 2009) and along walking/bicycle trails
(S. Gillingwater pers. comm. 2010). Planck and Planck (1977) observed snakes basking on top of
shingles and crawling underneath to forage for earthworms. Mating often takes place at basking
areas in close proximity to their hibernation sites, thus suitable habitat during this life process
consists of many of the above habitat types from open spaces in vegetation to grass thickets
(Harding 1997; Holman et al. 1999). In addition to basking sites, cooling sites are used by Butler’s
Gartersnake to lower body temperature during hot days in mid to late summer (LGL 2011).
Cooling sites include shady areas such as the base of mature thickets, dogwood bushes,
underground retreat sites, rock piles, large rocks, forest edges and shrubs, and various man-made
19
Hibernacula are subterranean structures (natural or man-made) that occur where conditions provide access below the
frost line and where adequate moisture exists (where snakes will not freeze or become dehydrated).
8Recovery Strategy for the Butler’s Gartersnake 2016
structures (Logier 1939; LGL 2010; LGL 2011). Locations along the edges of forested areas and
cultural thickets are frequently used as cooling sites or cover (LGL 2010), and underground dens
may also be used as shelters or dwelling places to avoid extremely hot periods in mid-summer
(Logier 1939; Carpenter 1952; Catling and Freedman 1980).
Movement (commuting and dispersal 20) Habitat
Butler’s Gartersnake populations have typically shown limited movements and high site fidelity
(Carpenter 1952; COSEWIC 2010; LGL 2010; AMEC 2013). In southern Michigan,
Carpenter (1952) found Butler’s Gartersnakes had an activity range of two acres (0.8 hectares). In
southern Ontario the species’ activity range has been found to be slightly larger at 1.6 hectares
(AMEC 2013). Carpenter (1952) found that individual snakes did not extend their movements over
the entire available habitat, but limited themselves to a smaller parcel. In mark-recapture studies
Butler’s Gartersnakes were frequently recaptured within 50 m of their original capture location and
often under the same coverboard (recapture distance of 0 m) (AMEC 2013, 2014). LGL (2010)
and AMEC (2013) found that Butler’s Gartersnakes exhibited localized movements within their
activity area at certain times of the year (e.g., bolting movements to and from live birthing sites
and hibernacula). Recent work by AMEC also showed that range lengths (maximum distance
moved in an active season) for non- relocated Butler’s Gartersnakes were between 150 – 380 m
(AMEC 2012, 2013, 2014). Movements across roads, through residential/landscaped areas or via
linear corridors such as drains were rare, and most individuals kept to the outer boundaries of
forested or wooded areas. Relocated individuals exhibited larger ranges, most likely due to
exploratory movements after release (AMEC 2013).
Though a clear outlier in comparison to all other recaptured snakes in the study, one snake was
recaptured 1,200 m from its initial capture site in Point Edward, Ontario (adjacent to Sarnia)
(J. Kamstra pers. comm. 2009). This behaviour may be a response to dry summer conditions and a
lack of available food. As temporary wet areas dry up in late spring and early summer, Butler’s
Gartersnakes are known to move to portions of their habitat where wet or moist areas remain
throughout the year (W. King pers. comm. 2014). Long linear movements of up to 250 m have
also been associated with movement from basking sites towards hibernacula in the fall
(AMEC 2013; M. Hazell pers. comm. 2014).
3.4 Biological Limiting Factors
Although some populations may still be relatively large, even within the City of Windsor, many
Butler’s Gartersnake subpopulations in Ontario are small and isolated, and the disjunct distribution
of this species indicates that it likely occupied a much wider range in the past (COSEWIC 2010).
This previous range is believed to have occurred under warmer, drier conditions and may suggest
that the species is limited by climate (Grand River Conservation Authority 2004). The tendency of
Butler’s Gartersnakes to typically move only short distances suggests that they may not attempt to
cross gaps between unsuitable habitats, making them susceptible to habitat fragmentation
(COSEWIC 2010). Butler’s Gartersnake has become quite dependent on earthworms as its
preferred food source, largely restricting its distribution to grassland habitats associated with wet
20
Commuting here refers to short-distance movement within the home range in order to complete different life stages
(e.g., foraging), while dispersal refers to long-distance movement related to emigration of individuals.
9Recovery Strategy for the Butler’s Gartersnake 2016
or moist areas supporting earthworms and possibly limiting its ability to colonize more arid
grasslands (Carpenter 1952; Lyman-Henley and Burghardt 1995).
The small subpopulation sizes of Butler’s Gartersnake in Ontario may limit the ability of the
species to adapt to environmental change and, as a result, subpopulations may be subjected to
higher extinction risks (Shaffer 1981; Reed et al. 2003; Santos et al. 2009) due to stochastic and
human related factors (Santos et al. 2009). Boulding and Hay (2001) indicate that environmental
changes can decrease population size, causing genetic variation to decrease. Decreased genetic
variation in combination with inbreeding depression, can limit further adaptive responses
(Hoffman and Willi 2008). Specific data on inbreeding depression in Butler’s Gartersnake are not
available, but studies focused on other snake species (e.g., Madsen et al. 1996) found that
inbreeding depression does occur and can cause reduced brood size and a high proportion of
unviable offspring. A simulation involving the Wisconsin population of Butler’s Gartersnake
found that populations with less than approximately 40-50 adult females begin to show
disproportionally higher risk of extirpation (Hyde et al. 2007). Hyde et al. (2007) also indicates
that reductions in survival of juveniles through inbreeding depression can have a major impact on
Butler’s Gartersnake population viability. That said, other recent studies show that some reptile
species are not affected by these genetic issues, suggesting that further work is needed.
10Recovery Strategy for the Butler’s Gartersnake 2016
4. Threats
4.1 Threats Assessment
Table 1. Threat Assessment Table
Level of Causal
Threat Extent Occurrence Frequency Severityb
Concerna Certaintyc
Habitat Loss, Degradation, or Fragmentation
Urban and industrial Historic/
High Widespread Recurrent High High
development Current
Agricultural practices,
Historic/
expansion and High Widespread Continuous High High
Current
intensification
Development of roads Historic/
and highways High Widespread Current/ Recurrent High High
Anticipated
Exotic, Invasive, or Introduced Species
Exotic and invasive Current/
species Medium Widespread Continuous Low Medium
Anticipated
Snake Fungal Disease Medium Widespread Unknown Unknown Unknown Low
Changes in Ecological Dynamics or Natural Processes
Subsidized predation Medium/Low Widespread Unknown Unknown Unknown Low
Disturbance or Harm
Direct persecution Medium/Low Widespread Unknown Unknown Unknown Low
Biological Resource Use
Collection for personal Historic/
Lowd Localized Recurrent Low High
use Current
a
Level of Concern: signifies that managing the threat is of (high, medium or low) concern for the recovery of the
species, consistent with the population and distribution objectives. This criterion considers the assessment of all the
information in the table.
b
Severity: reflects the population-level effect (high: very large population-level effect, moderate, low, unknown).
c
Causal certainty: reflects the degree of evidence that is known for the threat (high: available evidence strongly links
the threat to stresses on population viability; medium: there is a correlation between the threat and population
viability e.g. expert opinion; low: the threat is assumed or plausible).
d
Threats with a low Level of Concern are listed and described but may not be specifically addressed in the recovery
approaches.
4.2 Description of Threats
This section describes major threats outlined in Table 1, emphasizes key points and provides
additional information. Although threats are listed individually, an important concern is the
long-term cumulative effect of a variety of threats to local Butler’s Gartersnake subpopulations.
11Recovery Strategy for the Butler’s Gartersnake 2016
It should be noted that most of these threats are typically more harmful during the species’ active
season (generally April to September) because they lead to higher levels of direct mortality or
mutilation. Moreover, exposure to threats increases in periods in which Butler’s Gartersnake
movements increase, for example when some females move greater distances between hibernation
and live birthing areas in the spring. Some of these threats could also affect the species during the
non-active season, such as those that destroy or alter hibernacula.
Among the mechanisms through which threats can impact Butler’s Gartersnake populations,
isolation through habitat loss is of special concern, as it can lead to a breakdown of
metapopulation dynamics 21 and a reduction in genetic diversity and possibility of rescue effect 22.
Threats such as increasing urbanization, agricultural practices, the development of road networks,
and the spread of exotic or invasive species can all contribute to further isolation of remaining
subpopulations. Most threats including the various types of development can impact the species
significantly regardless of the time of year by eliminating habitat. Collection for personal use has
also been documented in Ontario (M. Hazell pers. comm. 2014) and subsidized predation and
direct persecution are believed to occur. Threats are listed in decreasing order of concern.
Urban and Industrial Development
Rare habitat types in Southern Ontario such as prairies and grasslands are quickly disappearing
due to an increasingly urbanized environment. Urbanization is a widespread threat and has resulted
in the documented loss of Butler’s Gartersnake locations in Michigan (T. Cox pers. comm. 2009 as
cited in COSEWIC 2010) and Ontario. Research conducted in 2009 within the Windsor – Sarnia
region identified eight previously known sites destroyed by development (COSEWIC 2010).
Other threats associated with increasing urban and industrial development include the frequent
mowing and management of lawns, and the destruction or alteration of natural and man-made
structures that are used by Butler’s Gartersnake for thermoregulation or hibernacula (COSEWIC
2010). Additionally, the drainage of wet areas (seasonal wetlands, small marshes, ponds) used by
Butler’s Gartersnakes may result from various development projects (Joppa and Temple 2005).
Agricultural Practices, Expansion and Intensification
Dense cover of grasses or herbs and a heavy thatch layer are essential habitat characteristics of
Butler’s Gartersnake (Planck and Planck 1977). The prevalence of intensive agricultural practices
in southwestern Ontario limits the establishment of Butler’s Gartersnake habitat. Continued
disturbances through tilling and ploughing prevent the establishment of grasses and thatch. The
expansion of agricultural land might also involve the drainage of seasonal wetlands, small marshes
and ponds which are often used by Butler’s Gartersnake. The conversion of snake habitat into
arable 23 land has been documented (COSEWIC 2010). In the 1980s a location within Essex
County, which was known as one of the largest local subpopulations of Butler’s Gartersnake, was
destroyed when it was converted to agricultural use (Planck and Planck 1977).
21
Short and long-term changes in the size and age composition of a group of spatially separated (sub)populations of
the same species which interact at some level (also known as a metapopulation), and the biological and environmental
processes influencing those changes.
22
The possibility for snakes to repopulate Ontario from the United States.
23
Cultivated by ploughing or tillage.
12Recovery Strategy for the Butler’s Gartersnake 2016
Pesticides and herbicides could negatively affect Butler’s Gartersnake because pesticides easily
find their way into soils and can be toxic to earthworms (Pimentel 2005), their main prey item.
A study conducted by Potter et al. (1990) found that pesticides can significantly decrease
earthworm populations. Casbourn et al. (1976) found a strong relationship between the number of
earthworms and density of Butler’s Gartersnake.
Development of Roads and Highways
An ever-expanding road network across southern Ontario has created a severely fragmented
landscape, increasing subpopulation isolation, reducing landscape connectivity, and threatening
the survival of this species across its range. Road networks fragmenting continuous tracts of
suitable habitat have a significant impact on Butler’s Gartersnakes, which already have a limited
home range (Carpenter 1952; Oliver 1955; DRIC 2009; COSEWIC 2010). Butler’s Gartersnakes
are particularly susceptible to road mortality (Sandilands 2001) because they are slow-moving in
non-vegetated areas (Ruthven 1904; Ontario Nature 2011), are small and very difficult for drivers
to see on roads, and can be attracted to the open habitat of road corridors for their thermal
properties. Although no detailed studies have investigated the effects of road networks on Butler’s
Gartersnake, road mortality has been observed across the species’ range (Harding 1997;
J. Choquette pers. comm. 2009 as cited in COSEWIC 2010; LGL 2010). One study that did
document road mortality in 2010 found multiple Butler's Gartersnakes killed on roads
(Choquette 2014), and dispersal of radio-tracked Butler's Gartersnakes appeared to be limited by
existing roads.
Exotic and Invasive Species
Exotic or invasive species have contributed to the loss of suitable habitat for Butler’s Gartersnake
(Hyde et al. 2007; Kapfer et al. 2013; Mifsud 2014). Although Butler’s Gartersnakes may readily
use small stands or patches of some non-native grass species; large, dense stands of European
Common Reed (Phragmites australis australis) and Reed Canary Grass (Phalaris arundinacea)
are not preferred, as they can alter habitat structure by shading basking sites and eliminating live
birthing areas (Kapfer et al. 2013; W. King pers. comm. 2014).
As Butler’s Gartersnake uses crayfish burrows as hibernacula, the invasion of Rusty Crayfish
(Orconectes rusticus) poses a potential threat, as it has been known to outcompete and displace
native crayfish species in Ontario and occurs within the Butler’s Gartersnake range (Hamr 1997;
Momot 1997). Although the effect of Rusty Crayfish on C. diogenes and F. fodiens is not yet
determined, a Wisconsin study found that occurrences of Rusty Crayfish heavily overlap with
occurrences of C. diogenes, as well as several other native crayfish (Olden et al. 2006). The
displacement of C. diogenes and F. fodiens could reduce the amount of suitable hibernation habitat
for Butler’s Gartersnake, as Rusty Crayfish generally do not dig burrows other than small pockets
under rocks and debris (Gunderson 2008).
Subsidized Predation
Predation by dogs and domestic and feral cats, as well as raccoons and skunks, may be a
significant threat (Loss et al. 2013). This is due to the large human population within the highly
urbanized portions of the Butler’s Gartersnake range in Canada, and the fact that Butler’s
Gartersnakes will use human-modified habitats. Recent research shows that feral cats are
13Recovery Strategy for the Butler’s Gartersnake 2016
a significant threat to reptile populations in the United States (Loss et al. 2013). Populations of
raccoons are dense in southern Ontario (approximately 1.1 million), especially around urban areas
where there is an estimated 8-18 raccoons per square kilometre (OMNR 2009).
Direct Persecution
Negative attitudes toward snakes are common throughout North America, and even harmless
species such as Common Gartersnakes are routinely killed (Gillingwater, pers. obs.) out of fear,
prejudice or ignorance (Choquette 2011). Although it is unclear how significant a threat human
persecution 24 is to the Butler’s Gartersnake, the risk of persecution is generally greater for snake
species that inhabit highly urbanized areas where the incidence of snake-human interaction is high
(Choquette 2011). Snakes regularly elicit reactions of fear or hostility from the general public, and
as a result, discriminate killing can be a significant source of mortality (Ashley et al. 2007).
Collection for Personal Use
There have been several instances of collection observed in Ontario, presumably for personal use
(M. Hazell pers. comm. 2014). While this threat may be of low concern to the species as a whole
(COSEWIC 2010), urban snake populations may be at greater risk due to the proximity of large
human populations.
Snake Fungal Disease
Another potential threat that may affect the Butler’s Gartersnake is Snake Fungal Disease (SFD)
(Ophidiomyces ophiodiicola) (Sleeman 2013). This is an emerging fungal disease in wild snakes
that causes severe skin lesions, leading to widespread morbidity and mortality (Sleeman 2013;
Allender et al. 2015). SFD is currently known to affect several species including the Northern
Watersnake (Nerodia sipedon), Eastern Foxsnake (Pantherophis gloydi), Eastern Milksnake
(Lampropeltis triangulum), and Massasauga (Sistrurus catenatus) (Sleeman 2013). SFD has been
confirmed in Ontario, in an Eastern Foxsnake found in southwestern Ontario in 2015 (Crowley
pers. comm. 2015). It has also been confirmed in nine states in the U.S., although it is considered
likely to be even more widespread (Sleeman 2013).
5. Population And Distribution Objectives
The population and distribution objective for Butler’s Gartersnake is to maintain the current
abundance and distribution of all extant subpopulations. Where biologically and technically
feasible, the distribution and abundance of extant subpopulations should be increased and habitat
connectivity between local subpopulations improved.
The above objective has been set recognizing that the abundance of this species is challenging to
determine due to the species’ habits. However, some effective methods for detecting this species
have been developed during the Herb Gray Parkway (HGP) project as discussed in section 3.2.
24
Human persecution of snakes occurs when people either fear or do not like the species. Many times persecution
results in snakes being intentionally killed, and contributes to lower population numbers or local extirpation of the
species.
14Recovery Strategy for the Butler’s Gartersnake 2016
Butler’s Gartersnake has recently been found in only two regions in Ontario: Windsor – Sarnia and
Luther Marsh. Additional surveys are needed to determine the presence/absence of the species in
two others, Skunk’s Misery and Parkhill, as well as nine unknown and four historical locations
throughout Windsor-Sarnia, including Walpole Island (COSEWIC 2010; J. Choquette pers. comm.
2014). As many Butler’s Gartersnake populations are disconnected within the species’ range, so
too are many of the local subpopulations found in urban areas in Ontario, such as the habitat in the
Windsor – Sarnia region. Some of the urban subpopulations numbers in particular may be below
sustainable levels. Because of this, increasing the area occupied by subpopulations, as well as
improving habitat connectivity between occupied habitats is vital for the survival of the species.
Increasing connectivity will also reduce the likelihood of a genetic bottleneck 25 within the species’
Canadian range.
6. Broad Strategies and General Approaches to Meet Objectives
6.1 Actions Already Completed or Currently Underway
Recovery actions described in the Draft Walpole Island Ecosystem Recovery Strategy (Bowles
2005) included raising awareness in the First Nation community about species at risk, including
Butler’s Gartersnake. Pamphlets, calendars, newsletter articles, posters and other promotional
material about species at risk have been prepared and distributed in the Walpole Island First
Nation community.
The general habitat for Butler’s Gartersnake was protected under the ESA when the species was
uplisted to Endangered in 2010.
In the Windsor area, the construction of a divided multi-lane highway, the HGP during the period
from 2011 to 2015 resulted in impacts to at least one subpopulation of Butler’s Gartersnake.
Portions of the Butler’s Gartersnake subpopulations in this area were formerly found in the
corridor being developed for the HGP during pre-construction surveys in 2010 and 2011. After
exclusion fencing was erected along the corridor, all snakes found within the fenced construction
area were relocated to adjacent habitat on the outside of the fence under a permit issued under the
provincial ESA.
Mitigation efforts for Butler’s Gartersnake included developing a restoration and management
plan. An ongoing mark/recapture radio telemetry study was initiated to study the effects of
mitigation measures and help determine key habitat areas for Butler’s Gartersnake including
hibernacula, live birthing habitat and movement corridors (LGL 2010; AMEC 2012, 2013, 2014).
An extensive monitoring program, which began in 2009, has been underway to determine impacts
to the subpopulations as a requirement of the permit. This includes monitoring activities such as
radio tracking snakes, assessing movement behaviours of displaced snakes, monitoring the
effectiveness of created habitat features (e.g., hibernacula, corridors, basking and cooling areas)
and expanding the baseline knowledge of subpopulation size, distribution and behaviour.
Monitoring activities will continue five years post-construction; the permit expires in 2021.
25
A sharp reduction in the size of a population due to environmental events (such as earthquakes, floods, fires, or
droughts) or human activities.
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